Liquid crystal displays (LCDs) have been used for several years now as a low-cost information display in e.g. calculators, watches, video games, audio and video equipment, portable computers, car dashboards, etc., i.e. especially in mobile devices wherein low weight is an important feature. Moreover, quality and size have been improved substantially so that LCDs are becoming an interesting alternative for the cathode ray tubes (CRTs) which are being used widely in television sets and desktop computer displays. In the meantime other flat panel display (FPD) types, such as plasma displays (PDs), field emission displays (FEDs) and organic light-emitting polymer displays (OLEDs) are attracting a lot of attention as potential alternatives of LCDs. Being emissive displays, PDs, FEDs or OLEDs may provide a solution for two major problems associated with LCDs, i.e. the low viewing angle and low efficiency (typically, only a few percent of the incident light or backlight passes through an LCD to form a readable image).
In all these FPDs, two glass plates are being used for carrying functional layers, e.g. electroconductive layers for pixel addressing, colour filters, liquid crystal orientation or alignment layers in LCDs or phosphor layers in FEDs and PDs. Between the two glass plates provided with said functional layers, there may be applied a filling, e.g. a liquid crystal compound (LCDs), a light-emmitting polymer (OLEDs) or a plasma-forming gas (PDs). After the assembly of such a sandwich, often called the display cell, one or more foils can be laminated to the outer surface of the glass substrate. In LCDs polariser foils are necessary components which are laminated to the glass substrate. In addition, several other types of foils are widely used to improve the image quality, e.g. retardation film, reflection or anti-reflection foils, foils which improve the viewing angle, light dispersion foils, etc.
Glass plates used in FPDs have a typical thickness in the range from 0.7 to 1.1 mm. Due to the high specific weight of glass, the total weight of a display is mainly determined by the size and thickness of these glass plates. In "Fourth-Generation LCDs--EIAJ Display Forecast", published in "Display Devices", Spring '96, Serial no. 13, p.14-19 (published by Dempa Publications Inc., Tokyo), it is emphasised that weight reduction of FPDs is a major need to be investigated. Weight reduction is important for mobile displays as well as for large stationary displays such as television sets and desktop computer displays. A further reduction of the thickness of the glass plates is however limited due to the high brittleness of such thin glass.
EP-A 759 565 describes a method wherein a functional layer is coated on a flexible, thin glass which is provided with a receiving layer of polycarbonate. Such a substrate is also very brittle since the receiving layer does not improve the probability of breakage.
For some low-cost applications, plastic sheets are being used as a low-weight substrate of an LCD. The high strength and flexibility of plastics even enables the making of a flexible display. However, the liquid crystal composition and other functional layers between said plastic sheets are not well protected from chemicals, oxygen, moisture, mechanical impact and other external influences and, as a result, the lifetime of such plastic displays is limited. In addition, plastics have a very low thermal and dimensional stability compared to glass, which are essential properties required for obtaining high quality displays.
Laminates of glass sheets and plastic foils are known in the art. A well known example is security glass used in car windshields as described in FR 2,138,021 and EP-A 669 205. The latter patent application describes a glass/plastic laminate comprising a glass pane, an intermediate adhesive layer and a plastic pane, wherein the glass has a thickness from 30 to 1000 .mu.m. The glass is preferably a chemically hardened glass and before lamination, a functional layer can be applied to the glass. After lamination, said functional layer is sandwiched between the glass and the plastic layer and is thereby protected from outside influences. A laminate of a thin chemically hardened glass and a plastic support has also been described in U.S. Pat. No. 3,471,365.